This invention relates to a dehydrator wherein a dehydration basket is driven by a variable speed motor so that the basket is rotated to dehydrate clothes contained in it.
The inventors have proposed a dehydrator such as a fully automatic clothes washing machine which is so arranged that an agitator and a wash and dehydration rotational tub serving as a dehydration basket containing clothes are driven by a variable speed motor. A dc brushless motor is employed as the variable speed motor in this arrangement. In a dehydration operation, the dc brushless motor is rotated at a predetermined rotational speed so that the rotational tub and the agitator are rotated at the predetermined rotational speed In this case the rotational speed of the dc brushless motor is controlled so as to be linearly increased until the predetermined rotational speed is reached after initiation of the dehydration operation.
In the above-described arrangement, control data for controlling the motor rotational speed is increased in a microcomputer-based control circuit controlling the motor rotational speed. The control data is representative of voltages applied to the -dc brushless motor.
However, noise is produced when the rotational speed of the dc brushless motor is increased by increasing the abovementioned control data, which noise gives a user an unpleasant feeling Further, the noise produced at the time of initiation of the dehydration operation is loud.
The inventors then tried to find the cause of the noise produced at the time the motor is accelerated. In the case where the motor is accelerated, the motor clanks every time the control data is increased. When the control data representative of a target rotational speed is supplied to the motor or when the voltage corresponding to the control data is applied to the motor, some period of time is required for the actual motor speed to reach the target rotational speed. Accordingly, the motor rotational speed is continuously increased every time the control data is increased. It is considered that clanking results from the continuous increase in the motor rotational speed. Since the motor rotational speed is continuously increased until a predetermined speed is reached after initiation of the dehydration operation, the motor clanks continuously, which causes a rumbling sound giving the user the unpleasant feeling.